For many companies and organizations, such as a chain of convenience stores, a public transit corporation, and a local government, it may be important to learn how the people move in a city or even cross cities. For these organizations, there are many key decisions relying upon the information of where the people are and where they come and go. Examples of such decisions include setting new bus routes, building new traffic stations, opening new stores, and building city facilities. Thus there is a need for a method for finding crowd movements.